This will get you to the open firmware screen. Transmac gives you a 15 day trial, which is plenty long enough to burn Leopard or whatever Mac image you plan on restoring.
In Transmac, open it in administrator mode, then right click the drive you want to put the image on, and select ‘restore from image’. On a mac use Disk Utility and the restore disk image feature to create the USB drive. You need to create the USB stick on a Mac, or with Transmac for PC.You cannot use a USB 3 stick, nor even a USB 3 port! You must use a USB 2 (or 1) drive and port.
For many years I always thought that booting from a USB stick was impossible on these systems, but alas it is very possible and not even that hard! You just have to do things a certain way. I love vintage macs, especially the PPC era macs like the iBook G4, and the Powerbook.
